TOKYO -- More than 500 million yen ($4.6 million at current rates) of the 58 billion yen in NEM virtual currency taken from Tokyo-based Coincheck has apparently been converted into such forms as bitcoin, making it more difficult to track.

A darknet website created Wednesday or earlier offers to exchange NEM for other cryptocurrencies. Police in Tokyo have made contact with someone who has used the site and confirmed that sending virtual currency as instructed yields NEM in return, according to a source involved in the investigation.

Transfers involving two wallets that Trend Micro suspects of being used for transactions via the darknet website picked up pace early Wednesday, according to the cybersecurity company. Around 300 transfers had been made by late Friday for NEM worth a total of around 500 million yen at the time of theft, suggesting that many people have agreed to the exchanges.

The NEM.io Foundation has tagged the NEM stolen from Coincheck, making the ill-gotten gains easy to track. By converting them into less traceable cryptocurrencies, the culprits are thought to be preparing to cash in their haul.